This invention relates generally to methods and devices used to treat arrhythmias. In particular, this invention relates to treatment of paroxysmal atrial fibrillation by electrical isolation of the pulmonary veins from the left atrium of the heart.
Atrial fibrillation is the most common form of cardiac arrhythmia and affects approximately 1.5 million patients in the United States annually, causing considerable morbidity as well as mortality. Additionally, atrial fibrillation is the leading cause of embolic stroke, leading to over 70,000 cerebrovascular failures per year.
There is extensive literature documenting the role of the pulmonary veins as the origin of excitatory impulses in patients with paroxysmal atrial fibrillation. There is a 70% cure rate in the treatment of paroxysmal atrial fibrillation and a 30% cure rate in the treatment of fixed atrial fibrillation when the pulmonary veins are electrically isolated.
Physicians may employ a variety of methods for treating patients with atrial fibrillation, including drug therapy, surgery and catheter ablation. Most patients prefer drug therapy because it is the most non-invasive treatment. However, drug therapy typically treats the symptoms of atrial fibrillation rather than the cause.
Several surgical techniques have been developed for the treatment of atrial fibrillation. These, techniques include implanting defibrillators or pacemakers or utilizing one of a variety of open-heart or percutaneous procedures to modify or inhibit cardio-electric impulses leading the atrial fibrillation. U.S. Pat. Nos. 5,531,779, 5,978,705, 6,094,596, and 6,275,730 disclose different surgical techniques in which defibrillators or pacemakers are implanted in the body to stimulate the heart in manner that prevents irregular rhythms. These implanted devices stimulate the heart at a slightly higher than normal rate in an effort to control the heart rate and avoid atrial fibrillation. However, implanting such devices requires invasive surgery and monitoring for post-implant complications.
The most common surgical procedure in the treatment of atrial fibrillation is the Maze procedure, originally developed by Dr. James L. Cox. When performing this procedure, first an electrophysiology study is conducted to map the electrical impulses and conduction pathways in the cardiac chambers and to determine the cardiac tissue that is causing the arrhythmia. Next, an open-heart or percutaneous procedure is used to make one or more controlled incisions in the wall of the left atrium running from the right and left superior pulmonary vein, following along both inferior pulmonary veins, and terminating at the annulus of the mitral valve. An additional incision is made connecting the superior ends of the first incisions, effectively isolating the pulmonary vein ostia from the remaining atria tissue by creating conductive blocks. While surgical techniques, such as the Maze technique, have proven successful is treating atrial fibrillation, they are highly invasive, generate a host of post-operative complications, require lengthy patient recovery times and are costly.
Thermal ablation techniques, such as radio frequency (RF) ablation and microwave ablation, have also been successful in treating atrial fibrillation. Thermal ablation typically involves the use of a catheter having one or more electrodes at or near its distal end. Once the catheter has been properly positioned in the atrium, the device is energized so as to evaporate water contained in the target tissue rendering it non-conductive. While thermal ablation has been successful in treating atrial arrhythmias, there are several problems associated with it. Microwave generators necessary for microwave ablation techniques tend to be prohibitively expensive for most catheter laboratories. RF generators produce electrical “noise” that interferes with the physician's ability to use electrocardiographic and other patient monitoring equipment during the ablation procedure. The catheters used in both types of thermal ablation tend to create coagulum at the distal tip, creating higher instances of cerebrovascular events due to the dislodged coagulum. Thermal ablation techniques also require meticulous tracking of electrical impulses with a second transeptally placed catheter. This is excessively time consuming. Finally, extensive ablation within the pulmonary veins themselves has led to pulmonary venous stenosis and pulmonary hypertension. To prevent the devastating effects of stenosis in all four pulmonary veins, thermal ablation is usually performed as two or more partial procedures, with a recovery period between surgeries, adding significant costs, patient time, and discomfort.
U.S. Pat. Nos. 6,266,563 and 6,397,109, U.S. patent application Nos. US 2003/0055491 (WO 03/003948), US 2003/0018362, and US 2003/0069606, and Bernstein et. al, Successful Stent Treatment of Pulmonary Vein Stenosis Following Atrial Fibrillation Rediofrequency Ablation, THE JOURNAL OF INVASIVE CARDIOLOGY, Jul. 2002, at 414, disclose various stenting techniques which attempt to address the problems associated with ablation procedures. Stenting has historically been used in interventional procedures as a means of maintaining the patency of a diseased conduit in the body. Stents are typically expandable tubular structures comprised of metals, metal alloys, composites, or polymers that are navigated through a conduit in the body, while secured to the distal end of a deployment catheter. Stents can be self expanding, or deployed with the aid of a balloon or other mechanical device. Stenting has been employed in several areas of the human body including peripheral and coronary arteries and veins, both biliary and bronchial trees, as well as in the ureters and fallopian tubes, for the sole purpose of maintaining the conduit's patency. While the combination of stenting either after or during the ablation process has been successful in treating atrial fibrillation, serious problems associated with the burning and scarring of the ablated tissue persist. The most common problem associated with stricture of the pulmonary vein after stenting and ablation is the backing up of blood in the lungs.
Despite the advances made in the treatment of atrial fibrillation, there continues to be a need for a non-invasive, inexpensive technique to prevent atrial fibrillation without creating post-operative or post-procedure complications. More importantly, there is the need for a preventative alternative to thermal ablation techniques to avoid pulmonary vein stenosis.